1. Field
The present application relates to the fields of pharmaceutical chemistry, biochemistry, and medicine. In particular, the present application relates to methods of making cationic steroidal antimicrobials (“CSAs” or “ceragenins”).
2. Related Technology
Endogenous antimicrobial peptides, such as the human cathelicidin LL-37, play key roles in innate immunity. LL-37 is found in airway mucus and is believed to be important in controlling bacterial growth in the lung. Antimicrobial peptides are found in organisms ranging from mammals to amphibians to insects to plants. The ubiquity of antimicrobial peptides has been used as evidence that these compounds do not readily engender bacterial resistance. In addition, considering the varied sequences of antimicrobial peptides among diverse organisms, it is apparent that they have evolved independently multiple times. Thus, antimicrobial peptides appear to be one of “Nature's” primary means of controlling bacterial growth. However, clinical use of antimicrobial peptides presents significant issues including the relatively high cost of producing peptide-based therapeutics, the susceptibility of peptides to proteases generated by the host and by bacterial pathogens, and deactivation of antimicrobial peptides by proteins and DNA in lung mucosa.
An attractive means of harnessing the antibacterial activities of antimicrobial peptides without the issues delineated above is to develop non-peptide mimics of antimicrobial peptides that display the same broad-spectrum antibacterial activity utilizing the same mechanism of action. Non-peptide mimics would offer lower-cost synthesis and potentially increased stability to proteolytic degradation. In addition, control of water solubility and charge density may be used to control association with proteins and DNA in lung mucosa.
With over 1,600 examples of antimicrobial peptides known, it is possible to categorize the structural features common to them. While the primary sequences of these peptides vary substantially, morphologies adopted by a vast majority are similar. Those that adopt alpha helix conformations juxtapose hydrophobic side chains on one face of the helix with cationic (positively charged) side chains on the opposite side. As similar morphology is found in antimicrobial peptides that form beta sheet structures: hydrophobic side chains on one face of the sheet and cationic side chains on the other.
We have developed small molecule, non-peptide mimics of antimicrobial peptides, termed ceragenins or CSAs. These compounds reproduce the amphiphilic morphology in antimicrobial peptides, represented above by CSA-13, and display potent, as well as diverse, biological activities (including, but not limited to anti-bacterial, anti-cancer, anti -inflammatory, promoting bone growth, promoting wound healing, etc.). Lead ceragenins can be produced at a large scale, and because they are not peptide based, they are not substrates for proteases. Consequently, the ceragenins represented an attractive compound class for producing pharmaceutically-relevant treatments.